1. Field of the Invention
The present invention relates to an optical member and a method of manufacturing the same. More specifically, the present invention relates to an optical member having a fine textured structure of an oxide on the surface and a method of manufacturing the same.
2. Description of the Related Art
For example, eyeglass lenses, optical lenses, solar panels, cathode-ray tubes, filters, and display panels are required to be low in light scattering and reflection of the surfaces thereof. As a method of achieving this requirement, a single- or multi-layer antireflection coating that is controlled in the refractive index and thickness is used. Such a case is known that the antireflection properties of the coating change depending on the wavelength and the angle of incidence and that the realization of high-performance antireflection properties in broad ranges of the wavelength and the angle of incidence is difficult.
In addition, it is known that fine textured formed on the surface of glass can impart an antireflection function to the glass. In particular, an antireflection function over a broad range of the angle of incidence can be expected if the texture is smaller than the wavelength. As methods for fining, chemical etching or mechanical processing of glass surfaces is proposed. In the chemical etching and the mechanical processing, a fineness smaller than the wavelength of visible light is difficult. Thus, chemical etching or mechanical processing that can realize antireflection properties for an application requiring transparency in wavelength of visible light has not been developed. Furthermore, a coating film forming a textured structure on a glass surface has been investigated. For example, in Japanese Patent Publication No. 61-48124, it is disclosed that an antireflection coating formed on a transparent material such as glass by converting a metal film of aluminum, magnesium, zinc, or an alloy thereof into an oxide or a hydroxide and that the antireflection coating constitutes discrete leeflets having various heights and shapes. Japanese Patent Laid-Open No. 9-202649 discloses a transparent alumina film that is randomly agglomerated like a petal. The film is formed by applying a coating solution containing at least an aluminum alkoxide and a stabilizer onto a substrate to form an amorphous alumina film, treating the film hydrothermally, and drying it.
Many coating films as shown in Japanese Patent Publication No. 9-202649 are generally porous. In general, glasses having a high refractive index used as base materials contain oxide components such as an alkali oxide, an alkaline earth oxide, or boric oxide that are low in resistance to water and humidity. If these glasses are used as a base material for coating, water or humidity in the air penetrates to the surface of the base material, and an alkali oxide, an alkaline earth oxide, or boric oxide contained in the base material is released to cause fogging or whitening of the surface or the interface thereof. In addition, in the case of porous oxides, especially their unstable components such as a water-soluble component and a component that is dissolved and redeposited in water undergo a hydration reaction when the base material having a surface layer of porous oxides is brought into contact with moisture. Thereby, optical characteristics are deteriorated with the lapse of time. Furthermore, dissolution or corrosion of such as decomposition caused by the porous oxide itself may occur under an atmosphere containing an acid.